1. Field of the Invention
The present invention generally relates to a beam scanning apparatus, and more specifically, to a beam scanning apparatus which projects a ray of light using a polarized cell.
2. Description of the Related Art
Generally, an image forming device such as a laser printer reproduces an image in a manner in which a ray emitted from a laser diode is focused on a photoconductive drum, forming a latent image thereon according to an image signal as received, and the latent image formed on the photoconductive drum is developed and then transferred onto a sheet of paper to be printed.
FIG. 1 is a schematic diagram showing a conventional laser scanning apparatus used in a laser printer.
Referring to FIG. 1, the laser scanning apparatus 100 includes a laser diode 105, a collimator lens 110, a cylinder lens 120, a polygon mirror 130, a driving device 140, an F-θ lens 150, a reflection mirror 160, a photoconductive drum 170, a horizontal synchronization mirror 180, and a light sensor 190.
The laser diode 105 emits a beam. The collimator lens 110 renders the beam emitted from the laser diode 105 into a parallel beam with respect to an optical axis.
The cylinder lens 120 makes the parallel beam from the collimator lens 110 into a linear beam parallel to a sub scanning direction. The polygon mirror 130 scans with the linear beam from the cylinder lens 120 while moving at a constant linear velocity, thus moving the beam at a constant linear velocity. The driving device 140 is a motor rotating the polygon mirror 130 at the constant speed.
The F-theta lens 150 has a fixed refractive index with respect to the optical axis and refracts the beam which is reflected from the polygon mirror 130 at a fixed angle towards the main scanning direction. The F-theta lens 150 adjusts the focus on a scanning surface after correcting the aberration of the beam reflected from the polygon mirror 130. The reflection mirror 160 reflects the beam from the Fθ lens 150 in a certain direction so as to scan the beam on the surface of the photoconductive drum 170.
The horizontal synchronization mirror 180 reflects the beam from the F-theta lens 150 to the light sensor 190.
The light sensor 190 receives the beam reflected from the horizontal synchronization mirror 180. An output signal from the light sensor 190 is used for scanning synchronization.
According to the conventional laser scanning apparatus 100, a scan line reflected from the polygon mirror 130 is incident on the photoconductive drum 170 in the main scanning direction, thereby forming the scan line. Multiple scan lines are also formed along the sub scanning direction, crossing at right angles with the main scanning direction while the photoconductive drum 170 is being rotated.
The light sensor 190 receives the beam reflected from the horizontal synchronization mirror 180 and thus adjusts horizontal synchronization. As a result, starting points of the scan lines are aligned, and thus, images of scan lines having less deviation in starting points can be produced.
In the conventional scanning apparatus 100, however, the F-theta lens 150 must be precisely disposed in order to produce images of scan lines having less deviation in starting points. Moreover, the laser scanning apparatus 100 is found to be less effective in that noise rises in accordance with the increased rotation speed of the driving device 140 for high speed printing. Furthermore, because the respective scan lines are formed by pixels, there is a limit in printing speed.